This invention relates to freezing apparatus and method, and in particular to the conversion into a solid particulate product of a flowable material capable of being frozen or to the freezing of discrete foodstuffs such as prawns, scampi and peas. The flowable material may for example be a dairy product (for example cream, milk or yoghurt), liquid egg, a soup, a pharmaceutical, a microbiological culture, or a puree.
Various prior proposals have been made for methods of freezing dairy products into discrete particulate form. GB-A-1 264 439 describes direct contact of egg or dairy produce with a liquefied gas refrigerant to give pop-corn-like particles. GB-A-1 376 972 describes a small scale system for production of pellets of egg by causing the egg to fall from nozzles into liquefied gas or refrigerant.
GB-A-2 092 880 discloses a method and apparatus for producing buoyant frozen pellets of liquid, preferably cream, by causing drops of liquid to fall onto or into a liquefied gas. GB-A-2 117 222 and U.S. Pat. No. 4,843,840 disclose methods and apparatus for producing discrete bodies of frozen liquid, eg cream, by passing a pulsating flow of the liquid into or onto a stream of liquefied gas.
One disadvantage of such apparatus and methods as described in the aforementioned prior proposals is that difficulties arise in obtaining economical utilisation of the liquefied gas particularly when there is a large demand for the particulate material.
It has been proposed in GB-A-2 023 789 to freeze seafood such as prawns or scampi by depositing the seafood on the outer surface of a rotary drum having a horizontal axis of rotation cooling the inner surface of the drum by exposure to a cryogenic medium such as liquid nitrogen and spraying liquid nitrogen directly onto the seafood. Such an apparatus is unsuitable for freezing liquids.